The present technology relates to a secondary battery-use active material including a plurality of active material particles as primary particles, to a secondary battery-use electrode and a secondary battery that use the secondary battery-use active material, and to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus that use the secondary battery.
Electronic apparatuses such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been demanded to further reduce the sizes and the weights of the electronic apparatuses and to achieve their long life. Accordingly, as an electric power source for the electronic apparatuses, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed.
In these days, it has been considered to apply such a secondary battery not only to the foregoing electronic apparatuses, but also to various applications. Examples of such other applications may include a battery pack attachably and detachably mounted on the electronic apparatuses or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, and an electric power tool such as an electric drill, and various applications other than the foregoing applications are considered.
Secondary batteries utilizing various charge-discharge principles to obtain a battery capacity have been proposed. In particular, a secondary battery utilizing insertion and extraction of an electrode reactant or a secondary battery utilizing precipitation and dissolution of an electrode reactant has attracted attention, since such a secondary battery provides higher energy density than lead batteries, nickel-cadmium batteries, and the like.
The secondary battery includes a cathode, an anode, and an electrolytic solution. The cathode contains an active material (a cathode active material) participating in electrode reaction (charge-discharge reaction). As the cathode active material, a lithium compound (such as LiCoO2) with a layered rock-salt crystal structure or a lithium compound (such as LiMn2O4) with a spinel crystal structure is widely used. In addition thereto, a polyanion-based compound, more specifically, a lithium compound (such as LiFePO4) with an olivine crystal structure, or the like is used (For example, see Patent Literature 1).
Since the kind, composition, and the like of the cathode active material exert a large influence on battery characteristics such as a battery capacity and cycle characteristics, various studies have been made on the kind, composition, and the like of the cathode active material.
More specifically, in order to increase a charging-discharging capacity at the time of large-current charge and discharge, powder of a lithium iron phosphate-based material supports a conductive microparticle (for example, see Patent Literature 2). The lithium iron phosphate-based material is represented by LizFe1-yXyO4 (where X is Mg or/and the like, 0≦y≦0.3, and 0<z≦1), and an oxidation-reduction potential of the conductive microparticle is nobler than an oxidation-reduction potential of the lithium iron phosphate-based material.
In order to obtain superior input-output characteristics, lithium transition metal composite oxide particles are composited with carbon material particles (for example, see Patent Literature 3). The lithium transition metal composite oxide is represented by LiMePO4 (where Me is a divalent transition metal).
In order to obtain a high discharging capacity, a lithium composite metal phosphate has a crystallite diameter of 35 nm or less (see Patent Literature 4). The lithium composite metal phosphate is represented by LixAyPO4 (where A is Cr or/and the like, 0<x<2, and 0<y≦1).
In order to increase a charging-discharging capacity, lithium iron phosphate particles are manufactured by mixing an iron oxide or/and the like with a lithium raw material and a phosphorus raw material, adjusting a agglomerate diameter of the resultant mixture, and then firing the mixture in an inert gas atmosphere (for example, see Patent Literature 5). In the iron oxide or the like, a ratio of Na or/and the like to Fe is from 0.1 mol to 2 mol both inclusive, and a ratio of Fe2+ to Fe is 40 mol % or less.
In order to obtain superior electron conductivity, a specific surface area of a complex of a compound represented by LixFePO4 (where 0<x≦1) and a carbon material is 10.3 m2/g or more (for example, see Patent Literature 6).
In order to improve input/output characteristics, a coating layer containing a carbon material is provided on a surface of a primary particle of a lithium complex oxoacid salt satisfying conditions such as a specific particle diameter distribution (for example, see Patent Literature 7). The lithium complex oxoacid salt is represented by LieM3fPO4 (where M3 is one or more of Group 2 to 15 elements, 0<e≦1, and 0<f≦1).
In order to achieve stable charge-discharge cycle performance, the oil feed amount of N-methyl-2-pyrrolidone with respect to a lithium phosphate compound coated with an electron conductive substance containing carbon is from 25 g/100 g to 35 g/100 g both inclusive (for example, see Patent Literature 8). The lithium phosphate compound is represented by LixM11-sM2sPO4 (where M1 is Fe or/and the like, M2 is one or more of Group 2 to 15 elements, 0≦x≦1.2, and 0<s≦1).
In order to obtain superior electrical conductivity, particles having a core and a coating are synthesized in the presence of a carbon source (conductive carbon) (for example, see Patent Literature 9). The core contains a compound represented by LixM1-yM′y(XO4)n (where M is a transition metal element, M′ is Mg2+ or/and the like, X is P or/and the like, 0≦x≦2, 0≦y≦0.6, and 1≦n≦1.5).